RESEARCH FUNDAMENTALS Measurement instruments 2276 Am J Health-Syst Pharm—Vol 65 Dec 1, 2008 RESEARCH FUNDAMENTALS Validity and reliability of measurement instruments used in research CAROLE L. KIMBERLIN AND ALMUT G. WINTERSTEIN CAROLE L. KIMBERLIN, PH.D., is Professor; and ALMUT WINTERSTEIN, PH.D., is Associate Professor, Department of Pharmaceutical Outcomes and Policy, College of Pharmacy, University of Florida, Gainesville. Address correspondence to Dr. Kimberlin at the Department of Pharmaceutical Outcomes and Policy, College of Pharmacy, University of Florida, P.O. Box 100496, Gainesville, FL 32610 (kimberlin@cop.ufl.edu). The authors have declared no potential conflicts of interest. Copyright © 2008, American Society of Health-System Pharma- cists, Inc. All rights reserved. 1079-2082/08/1201-2276$06.00. DOI 10.2146/ajhp070364 Purpose. Issues related to the validity and reliability of measurement instruments used in research are reviewed. Summary. Key indicators of the quality of a measuring instrument are the reliability and validity of the measures. The process of developing and validating an instrument is in large part focused on reducing error in the measurement process. Reliability esti- mates evaluate the stability of measures, internal consistency of measurement instruments, and interrater reliability of instrument scores. Validity is the extent to which the interpretations of the results of a test are warranted, which depends on the particular use the test is intended to serve. The responsiveness of the measure to change is of interest in many of the applications in health care where improve- ment in outcomes as a result of treatment is a primary goal of research. Several issues may affect the accuracy of data collected, such as those related to self-report and sec- ondary data sources. Self-report of patients or subjects is required for many of the measurements conducted in health care, but self-reports of behavior are particularly subject to problems with social desirability biases. Data that were originally gathered for a different purpose are often used to an- swer a research question, which can affect the applicability to the study at hand. Conclusion. In health care and social sci- ence research, many of the variables of interest and outcomes that are important are abstract concepts known as theoretical constructs. Using tests or instruments that are valid and reliable to measure such con- structs is a crucial component of research quality. Index terms: Control, quality; Data collec- tion; Errors; Methodology; Research Am J Health-Syst Pharm. 2008; 65:2276-84 M easurement is the assigning of numbers to observations in order to quantify phenom- ena. In health care, many of these phenomena, such as quality of life, patient adherence, morbidity, and drug efficacy, are abstract concepts known as theoretical constructs. Measurement involves the opera- tionalization of these constructs in defined variables and the develop- ment and application of instruments or tests to quantify these variables. For example, drug efficacy may be operationalized as the prevention or delay in onset of cardiovascular disease, and the related measurement instrument may ascertain data on the occurrence of cardiac events from patient medical records. This article focuses primarily on psychometric issues in the measurement of patient- reported outcomes. However, similar aspects of measurement quality apply to clinical and economic out- comes. Steps to improve the mea- sures used in pharmacy research are also outlined. Evaluating the quality of measures Key indicators of the quality of a measuring instrument are the reli- ability and validity of the measures. In addition, the responsiveness of the measure to change is of interest in many health care applications where improvement in outcomes as a result of treatment is a primary goal of research. Data sources for measures used in pharmacy and medical care research often involve patient ques- tionnaires or interviews. Measures using patient self-report include quality of life, satisfaction with care, adherence to therapeutic regimens, symptom experience, adverse drug effects, and response to therapy (e.g., pain control, sleep disturbance). In addition, measures can be developed